Dometic RM5380 fridge won’t stay lit on gas

[robdav]

That was the button I was keeping pressed in using the selfie stick.

 

We're using Gaslow, so LPG/Autogas and have had two years, all seasons, of no problems with the fridge on gas. We're not normally on hook-up. I have been reading researching about Gaslow and Dometic fridges, see the end of this post https://www.motorhomefacts.com/forum-printtopic-1-62085-0-0-asc-viewresult-1.html

 

I wondering if the jet might still be the problem because even after I cleaned it with brake cleaner, there was still some black in it, as per previous photo?

[Derek Uzzell]

Based on the ‘look’ of the flame shown in the photo attached to your posting of 27 April 2021 5:52 PM, it’s most unlikely that there’s anything intrinsically wrong with the gas-jet itself that might obstruct the flow of gas.

 

A full fridge service would normally include replacement of the jet, rather than cleaning it, and poking anything (eg. a needle or a piece of thin wire) through the jet’s central hole is very bad practice. But as you’ve only used brake-cleaner when you’d removed the jet, that should have done no harm.

 

I suppose there’s the possibilty of there being debris ‘upstream’ of the jet that the pressure of gas blows against the jet and blocks the hole and you could try taking the jet out again and using a vacuum cleaner to suck out anything lurking in the pipework leading to the jet - but I’m doubtful that’s the cause of the problem.

 

The MHFacts thread you’ve linked to is 2009-vintage, and there’s been plenty of online discussions about using autogas to fuel 3-way fridges (some O&AL forum threads here)

 

https://tinyurl.com/4b6ru75z

 

Thetford does not forbid use of autogas, but does advise that a filter be fitted to guard against impurities finding their way through to a fridge. Autogas is intended to fuel vehicles not power leisure-vehicle gas appliances designed to operate using gas having a high degree of cleaniless, but owners of motorhomes with fixed LPG tanks (or who choose to have user-refillable gas bottles) rarely mention problems that might possibly be due to autogas ‘quality’. It may be that, if a filter is not fitted (and most motorhomes won’t have one) a fridge’s flue and gas-burner may need more regular cleaning than if ‘bottled gas’ were used, but that’s about it.

 

(Obviously you could try replacing the jet, but I don’t believe that’s where the problem lies.)

[Robinhood]

Whilst the proportion of propane in "Autogas" varies by country (AIUI, in the UK it is always 100% propane), there generally should always be a high enough proportion to avoid the sort of issue I alluded to in the relatively temperate UK winter.

 

Over the years, Dometic have varied their advice on gas use - the maintenance manual for my 8xxx series fridge/freezer contains the following:

 

2.5.1 Cleaning of burner

 

The burner and the chimney must be cleaned

regularly, at least one time a year.

If Autogas is used, Dometic recommends a

maintenance every half year, as the contamination

risk of the burner is higher, due to the burning

of the auto gas.

 

...but I'd agree with Derek that your pictures don't, at face value, look like you have a problem there.

[robdav]

Feeling a bit stuck in the unknown.

 

Can someone explain to me how the gas is 're-lit' when the fridge drops in temperature and the thermostat calls for more cooling?

 

I understand there isn't a permanent pilot light, like in the old days? So how is the burner re-ignited, what is the process?

 

I know this probably isn't related to the problem, I'm just trying to fill in the blanks in my knowledge to see if it helps with the diagnosis, on my part.

 

Thanks again, Rob

[_Chris]

I'm no expert in refrigeration but here is a diagram that I lifted from this website on how a 3 way fridge works.

 

https://www.campertrailers.org/3-way_fridge.htm

 

I think that re-lighting of the burner is controlled electronically.

 

 

[Ocsid]

robdav - 2021-04-28 12:27 PM

 

Feeling a bit stuck in the unknown.

 

Can someone explain to me how the gas is 're-lit' when the fridge drops in temperature and the thermostat calls for more cooling?

 

I understand there isn't a permanent pilot light, like in the old days? So how is the burner re-ignited, what is the process?

 

I know this probably isn't related to the problem, I'm just trying to fill in the blanks in my knowledge to see if it helps with the diagnosis, on my part.

 

Thanks again, Rob

I was thinking along the same line, if the thermostat's involvement does not involve reignition, it must surely modulate the gas flow, thus flame size and heat output.

 

Is that modulation, or switching the level of the flame "high" to "low" related to the flame out in anyway?

 

Does the "low" flame level even sustain any flame?

 

I can only envisage the low level flame involves a device to restrict the feed to the jet?

From that is that restricted route not working, eg a solenoid not acting, or its restriction it introduces blocked?

 

How that can be explored: if the fridge was taken way down on electricity, then attempted on gas we might expect the gas stat to intervene if not on ignition not long after? If when switching to gas we turned the stat up to the warmer extreme, that ought provoke it dropping to low level flame quite promptly

 

Or maybe the thermostat acts differently on gas than I am assuming, though I can't see another technique other than flame size modulation, whilst still burning to avoid tripping the flame failure device, in systems without reiginite.

[Keithl]

Ocsid - 2021-04-28 1:39 PM

 

Or maybe the thermostat acts differently on gas than I am assuming...

I didn't think the thermostat had any effect when operating on gas. It is either turned on or off, and this is it!

 

I was always under the impression that the thermostat was only functional when on 230 volts supply and maybe not even when on 12 volts.

 

Scrub that. From the instructions previously posted...

 

"For AC and gas operation, the thermostatic control ensures that the refrigerator temperature is kept constant and as little power as possible is consumed."

 

Keith.

[Keithl]

Robdav,

 

Does the 'Flame indicator' on the display panel move when the burner is alight?

 

Keith.

[robdav]

Keith

 

From recollection, when the fridge worked perfectly on gas, the indictor used to go most of the way to the right.

 

Since it has been unreliable, it seems to vary, but in my mind it doesn't go as far to the right as it used to.

 

What controls that? Why would it vary?

 

PS I've just tried cleaning the jet again with 99.9% alcohol this time but still the same problem.

 

 

[Derek Uzzell]

Dometic’s English-language Operating Instructions for a RM5380 fridge confusingly say

 

"The refrigerator is equipped with an automatic pilot light which automatically interrupts the gas supply after approx. 30 seconds if the flame goes out.”

 

but the German and French-language versions make it clear that the ‘pilot light’ is just a flame-failure safety feature.

 

The Instructions for gas operation are as shown on the image attached below and include advice on use of LPG (Autogas).

 

I can’t find anything in either the Installation or Operating Instructions to suggest that a RM5380 fridge operating on gas will attempt to auto-relight if the gas-flame goes out. This suggests that the flame’s intensity will be regulated according to the fridge’s cooling requirements and - when running normally on gas - the flame will stay continuously alight. As gas ignition is via a small AA battery, it might not be too surprising to find that there’s no auto-relight feature.

 

In the 2019 forum thread Rob refers to in his original posting I said

 

"The gas side of modern 3-way fridges does not involve a pilot-light, and the gas-burner turns on and off automatically. It sounds like the RM5380’s gas-burner may be turning off but failing to relight when it should, which might indicate an electrical fault. That’s just a guess though as the problem needs to be addressed professionally.”

 

but auto-relighting seems to be missing from the technical specification of RM5310, RM5330 and RM5380 fridges.

[robdav]

What does this device do?

 

https://www.jacksonsleisure.com/caravan/motorhome/dometic/spares/fridge/igniter/

 

Ignore that - it obviously takes the signal from the AA battery in the igniter button and turns it into a spark for the burner.

 

[robdav]

The second entry on this post is intriguing.

 

https://www.motorhomefun.co.uk/forum/threads/dometic-rm5380-fridge-noisy-on-gas.116390/

 

I am struggling to work out how the temperature inside the fridge is monitored.

[Derek Uzzell]

I’d expect (as said on the MHFun link) that there will be an inconspicuous sensor inside the fridge close to the finned ‘evaporator’ (probably near to where I’ve arrowed on the image attached below). The sensor will connect to a component outside the fridge’s interior that will monitor the temperature inside the fridge and (in the case of a RM5380) adjust the amount of gas fed to the burner.

[Ocsid]

Derek Uzzell - 2021-04-28 4:58 PM

 

I’d expect (as said on the MHFun link) that there will be an inconspicuous sensor inside the fridge close to the finned ‘evaporator’ (probably near to where I’ve arrowed on the image attached below). The sensor will connect to a component outside the fridge’s interior that will monitor the temperature inside the fridge and (in the case of a RM5380) adjust the amount of gas fed to the burner.

Which returns to the question I posed, does that "whatever" that "adjust the amount of gas fed to the burner", simply adjust it too low to sustain a flame adequate to hold the flame failure device from chopping things?

If that device is suffering gunging up, there could be simply too little gas passing to hold the flame.

[robdav]

I have a theory and have ordered a part.

 

I will report back whether it works (or not) next week sometime.

 

Thanks for all the help.

 

Rob

[robdav]

UPDATE – Fixed, it was the jet after all! Despite having both brake cleaner and 99.9% alcohol dripped through it and blown with compressed air, it wasn’t enough to clean it. Sometimes these jets can’t be cleaned, I guess.

 

I’m providing the rest of this update hoping it might help someone else.

 

The fridge is an RM5380 fitted in a 2018 panel van conversion. According to the Grove parts document here http://www.groveproducts.co.uk/medias/documents/grove/cata/Z-%20SPARES%20DOMETIC.pdf it lists jets for the RM5310 and the RM5330 as item 110, part number 289048300. However, the part list for the exact model of my fridge does not list a jet part (see first attached photo for difference). The jet is also quite different to the ‘old’ style as it’s not a separate insert. It’s actually a brass jet/hex nut all in one (see second photo – top old, bottom new?). I therefore had to replace the entire burner unit and effectively switch it back to the old-style jet and it’s now working perfectly.

 

I used this part:

 

http://www.swordcrowncaravans.com/index.php?route=product/product&product_id=1853&search=289056796 - Dometic fridge burner assembly CBS1 Piezo KZ65

 

HOWEVER, in hindsight I should have probably used this one (probably newer model):

 

http://www.swordcrowncaravans.com/index.php?route=product/product&product_id=1601&search=289060489 - Dometic fridge burner complete CBS2B DN65 PIEZ

 

Regardless, this begs the questions what does the ‘CBS’ bit relate to and what’s the difference between KZ65 and DN65, clearly it’s the jet format but why the change Dometic? Anyone know?

 

If anyone can find a part listing for a separate DN65 nozzle/jet then I’d be interested to know. Hope this helps someone!